Apparatus for mixing

ABSTRACT

The present invention relates to an apparatus for mixing of a chemical medium in gaseous or liquid state with a pulp suspension. The apparatus comprises a housing having a wail ( 2 ) that defines a mixing chamber ( 4 ), a first feeder ( 6 ) for feeding the pulp suspension to the mixing chamber, a rotor shaft ( 8, 104, 204, 300, 406, 502 ), that extends in the mixing chamber, a drive device for rotation of the rotor shaft, a rotor body ( 10, 200, 407, 504 ), that is connected to the rotor shaft and arranged to supply kinetic energy to the pulp suspension flow, during rotation of the rotor shaft by the rotation of the drive device, such that turbulence is produced in a turbulent flow zone ( 12 ) in the mixing chamber, a second feeder ( 13 ) for feeding of the chemical medium to the mixing chamber, and an outlet for discharging the mixture of chemical medium and pulp suspension from the mixing chamber.

The present invention relates to an apparatus for mixing of a chemicalmedium in gas gaseous or liquid state with a pulp suspension.

In treatment of pulp suspensions there is a need for intermixture ofdifferent mediums for treatment, for example for heating or bleachingpurposes. Therefore it is desirable to disperse the medium in the pulpsuspension during simultaneous conveyance of the pulp suspension througha pipe. Patent EP 664150 discloses an apparatus for this function. Forheating of pulp suspensions, steam is added which condense and therewithgive off its energy content to the pulp suspension. A bleaching agent isadded in bleaching that shall react with the pulp suspension. Inconnection to the treatment of recovered fibre pulp printing ink isseparated by flotation, which means that air shall previously bedisintegrated in the pulp suspension such that the hydrophobic ink, orthe printing ink, may attach to the rising air bubbles. In thisconnection it is desirable that the medium for treatment, e.g. air, isevenly and homogeneously distributed in the pulp suspension, preferablywith tiny bubbles to achieve a large surface against the pulpsuspension.

In all cases it is hard, with proportionately low addition of energy, toachieve an even intermixture of the medium in the flow of material. Whenheating pulp suspensions by supply of steam to a pulp pipe, problemsoften arise with large steam bubbles that are formed on the inside ofthe pipe, this as a consequence of a non-disintegrated gas with smallcondensation surface. When these large steam bubbles rapidly implodes,condensation bangs arises that causes vibration in the pipe and infollowing equipment. This phenomenon limits the amount of steam that canbe added to the system and thus the desired increase in temperature. Itis hard to achieve a totally even temperature profile in the pulpsuspension when large steam bubbles exists. In order to remedy theseproblems, a large amount of energy can be supplied to carefully admixthe steam in the pulp suspension. Another variant is to disintegrate thesteam already at the supply in the pulp suspension. In intermixing ofbleaching agent in a pulp suspension, relatively large amounts of energyare used in order to provide that the bleaching agent is evenlydistributed and conveyed to all the fibres in the pulp suspension. Theenergy requirements are controlled by which bleaching agent that shallbe supplied (rate of diffusion and reaction velocity) and also by thephase of the bleaching medium (liquid or gas). The geometry at supply ofthe bleaching agent in vapour phase is important in order to avoidunwanted separation immediately after the intermixture.

The object with the present invention is to provide an apparatus forsupplying and intermixing of a chemical medium in a pulp suspension inan effective way and that at least partly eliminates the above mentionedproblem.

This object is achieved with an apparatus for mixing of a chemicalmedium in gaseous or liquid state with a pulp suspension according tothe present invention. The apparatus comprises a housing having a wallthat defines a mixing chamber and a first feeder for feeding the pulpsuspension to the mixing chamber. Further, the apparatus comprises arotor shaft, that extends in the mixing chamber, a drive device forrotation of the rotor shaft and a rotor body that is connected to therotor shaft. The rotor body is arranged to supply kinetic energy to thepulp suspension flow, during rotation of the rotor shaft by the rotationof the drive device, such that turbulence is produced in a turbulentflow zone in the mixing chamber. The apparatus also comprises a secondfeeder for feeding of the chemical medium to the mixing chamber and anoutlet for discharging the mixture of chemical medium and pulpsuspension from the mixing chamber. The apparatus is characterised bythat the second feeder comprises at least one stationary feeding pipe,that extends from the wall of the housing into the mixing chamber andthat has an outlet for the chemical medium in or in close vicinity tosaid turbulent flow zone.

In that respect, in accordance with present invention, an even andeffective intermixing of the chemical medium in the pulp suspension isprovided.

Further features and advantages according to embodiments of theapparatus according to the present invention are evident from the claimsand in the following from the description.

The present invention shall now be described more in detail inembodiments, with reference to the accompanying drawings, withoutrestricting the interpretation of the invention thereto, where

FIG. 1 shows an apparatus in cross-section according to an embodiment ofthe present invention,

FIG. 2A shows in a cross-section a rotor shaft extending through afeeding pipe, which is coaxially arranged with the rotor shaft,

FIG. 2B shows in a cross-section a rotor shaft extending through afeeding pipe, which is eccentrically arranged with the rotor shaft,

FIG. 3A-E illustrates in cross-section different alternative outlets offeeding pipes,

FIG. 4A shows a symmetrical arranging of an outlet of a feeding pipearound a rotor shaft,

FIG. 4B shows an asymmetrical arranging of an outlet of a feeding pipearound a rotor shaft,

FIG. 4C shows non-rotational symmetrical outlets of a feeding pipearound a rotor shaft,

FIG. 5A-C illustrates different alternative embodiments of rotor pins incross-section of the rotor shaft,

FIG. 6A-D illustrates different alternative cross-sections of rotorpins,

FIG. 7A-C shows schematically alternative embodiments of a rotor shaftprovided with axial flow-generating elements,

FIG. 8A-D shows schematically alternative embodiments of flow passagesin an axial direction of a flow-restraining disk,

FIG. 9A-B shows alternative located patterns of flow passages for aflow-restraining disk,

FIG. 9C shows in one embodiment a flow-restraining disk in axialdirection comprising concentrically rings which are coaxial with a rotorshaft, and

FIG. 10A-D illustrates alternative embodiments of flow-restraining disksintegrated with the rotor shaft.

In FIG. 1 is shown an apparatus according to an embodiment of thepresent invention. The apparatus comprises a housing with a wall 2 thatdefines a mixing chamber 4 and a first feeder 6 for supplying of pulpsuspension to the mixing chamber. Further, the apparatus comprises arotor shaft 8, which extends in the mixing chamber 4, a drive device(not shown) for rotation of the rotor shaft and a rotor body 10 that isconnected to the rotor shaft 8. The rotor body is arranged to supplykinetic energy to the pulp suspension flow, during rotation of the rotorshaft by the rotation of the drive device, such that turbulence isproduced in a turbulent flow zone 12 in the mixing chamber. Theapparatus also comprises a second feeder 13 for feeding of the chemicalmedium to the mixing chamber and an outlet (not shown) for dischargingthe mixture of chemical medium and pulp suspension from the mixingchamber 4. The second feeder 13 comprises at least one stationaryfeeding pipe 14, that extends from the wall 2 of the housing into themixing chamber 4 and that has an outlet 16 for the chemical medium in orin close vicinity to said turbulent flow zone 12. The second feeder 13may comprise a number of stationary feeding pipes 14, as evident fromFIG. 1, that extends substantially parallel to the rotor shaft 8 in themixing chamber. Further, according to a not shown embodiment, thefeeding pipes 14, respectively, may extend substantially radially to therotor shaft 8 in the mixing chamber.

In case the feeding pipe 14 extend parallel to the rotation shaft, therotation shaft 8 may extend through the feeding pipe 14, whereby anannular outlet for chemical medium is defined by the rotor shaft 8 andthe feeding pipe 14. In that respect, a feeding pipe 102 can extendcoaxially as shown in FIG. 2A, or eccentrically to a rotor shaft 104 asshown in FIG. 2B, whereby an annular outlet 100 for the chemical mediumis defined by the rotor shaft 104 and the feeding pipe 102.

The outlet 16, 100 of the feeding pipe is suitably of rotationalsymmetrical design, such as a circular form as shown in FIG. 3A. Theoutlet of the feeding pipe may also be of other non-rotationalsymmetrical design, e.g. elliptical according to FIG. 3B-C, triangularform according to FIG. 3D, or rectangular form as shown in FIG. 3E.

In case the second feeder comprises a number of stationary feeding pipes14, the outlets 16 of the feeding pipes 14 can be situatedsymmetrically, on equal distance R from the rotor shaft 8, as shown inFIG. 4A, or asymmetrically around the rotor shaft 8, with differentdistance R1 and R2, respectively, from the rotor shaft 8, as shown inFIG. 4B. In case the outlets 16 of the feeding pipes, respectively, arenon-rotational symmetrical designed, at least one of the outlets 16 beprovided with an orientation of rotation V1 in relation to the centre ofrotor shaft that differs from the corresponding orientations of rotationV2 of the other outlets, as evident from FIG. 4C.

FIG. 5A-C illustrates that a rotor body 200 according to the presentinvention may comprise a number of rotor pins 202, which extends fromthe rotor shaft 204 in its radial direction. Each rotor pin may becurved forward from the rotor shaft (FIG. 5A) or backward (FIG. 5B)relatively to the rotational direction of the rotor body (see arrow inFIG. 5A-C), which both embodiments aims to provide a radial conveyanceof the mixture. According to an alternative embodiment shown in FIG. 5C,each rotor pin may have a width b, as seen in the rotational directionof the rotor body, that increase along at least a part of the rotor bodyin direction against the rotor shaft 204. The embodiment according toFIG. 5C decreases the opened area and by that the axial flow velocityincreases. The rotor pins 202 can be provided with varyingcross-sections as illustrated in FIG. 6A-D. Each rotor pin may bedesigned with a circular cross-section as shown in FIG. 6A, which issimple from a manufacturing viewpoint and a cost efficient design. Therotor pins 202 may also be provided with a triangular or quadraticcross-section, according to FIG. 6B-C, which geometry creates a dead airspace at rotation of the rotor shaft. According to yet an embodiment therotor pins may be provided with a shovel-shaped cross-section accordingto FIG. 6D, which results in a sling-effect at rotation of the rotorshaft. In addition, as evident from FIG. 6C, each rotor pin may bedesigned with a helix shape, suitably with quadratic cross-section, inthe axial direction of the rotor win. Which one of the various designsof the cross-sections of the rotor pins 202 that are most preferabledepends on the current flow resistance.

FIG. 7A-C shows alternative embodiments of a rotor shaft 300 providedwith one or more axially flow generating elements 302. As is shown inFIG. 7A, the axial flow-generating element can comprise a number ofblades 304, which are obliquely attached relatively to the rotor shaft.Rotation of the rotor shaft causes an axial flow. If the elements are ofvarious rotational orientations along the rotor shaft as shown in FIG.7A, different directions of flow are obtained as well. In addition, theaxial flow-generating element can comprise a screw thread or a bandthread 306, according to alternative embodiments shown in FIG. 7B-C,which extends along the rotor shaft 300, that aims to force the fluidclosest to the hub of the rotor shaft towards some direction. For thefeeding, the height of the band can suitably be about 5-35 mm. Accordingto an alternative embodiment the axial flow-generating element cancomprise a relatively thin elevation of about 3-6 mm on the surface ofthe shaft, suitably about 3.8 to 5.9 mm. This scale of lengths issuitably when it corresponds to the characteristic size of thefibre-flocks for kraft pulp at current process conditions. Thus, thisshould be variable in the process. The size of the flocks can be said tobe in inverse proportion to the total work that is added to the fibresuspension. Screw thread or band thread may be used also when the rotorshaft extends through the feeding pipe as shown in embodiments in FIG.2A-B, if the height of the band is relatively short.

Preferably, the apparatus comprises a flow-restraining disk 400 with onor more flow passages, having constant axial area, arranged totemporarily increase the flow velocity of the pulp suspension when thepulp suspension passes the flow-restraining disk. The purpose of thedisk is to create a controlled fall of pressure. The energy is used forstatic mixing and the disk is designed for varying pressure recoverydepending on desired energy level. FIG. 8A-D shows different alternativeembodiments of flow passages 402 in the axial direction of aflow-restraining disk 400. The flow area A of each flow passageincreases or decreases in the direction of the flow, which in particularis shown in FIG. 8A-B. FIG. 8A shows a divergent opening, i.e. that anopen area enlarges in axial direction. FIG. 8B shows a convergingopening, i.e. where the open area diminish in axial direction. As shownin FIG. 8C-D, each flow passage can extend obliquely from the up-streamside of the disk against the centre axis C of the disk.

The flow-restraining disk 400 is preferably provided with a plurality offlow passages 402 as shown in FIG. 9A-C, which passages can be arrangedaccording to a number of alternative placement patterns, radially spreadout on the flow-restraining disk. The disk is preferably circular orcoaxial with the rotor shaft. The flow passages of the flow-restrainingdisk may for example form a Cartesian pattern (FIG. 9A) which providesasymmetrical jet streams, or a polar pattern (FIG. 9B). FIG. 9C shows analternative embodiment where the flow passages 402 of theflow-restraining disk 400 in axial direction are foamed ofconcentrically rings 404 that are coaxial with a rotor shaft 406, andits rotor body 407, which may comprise one or more rotor pins 408,arranged on distance from and ahead of disk 400. The flow-restrainingdisk is suitably stationary arranged in the housing and the disk maycomprise a number of concentrically rings 404, which are coaxial withthe rotor shaft 406, and at least one radial bar 410, that fixates therings 404 relatively each other and that are attached in the wall of thehousing, whereby the flow passages 402 are defined by the rings and thebar.

However, a flow-restraining disk 500 can be integrated with the rotorshaft 502. FIG. 10A-D illustrates alternative embodiments offlow-restraining disks 500 integrated with the rotor shaft 502. Therotor body 504 may suitably comprise a number of rotor pins 506, whichextends from the rotor shaft 502, whereby the disk is fixed to the rotorpins 506 on the down-stream side of the rotor body as shown in FIG. 10A,or on its up-stream side as shown in FIG. 10B. As shown in FIG. 10C, therotor body may comprise an additional number of pins 506′, that extendsfrom the rotor shaft on-the down-stream side of the disk, whereby thedisk 500 also is fixed to said additional pins 506′. Preferably, thedisk comprise a number of concentrically rings 508, which are coaxialwith the rotor shaft, and the rotor pins 506, 506′ fixates the rings 508in relation to each other, whereby flow passages 510 are defined by thepins and the rings. FIG. 10D shows rotor pins 506 and concentricallyrings 500. Further, spacer elements 511 are arranged between the rotorpins 506 and the concentrically rings 500. The spacer elements are usedin order to move the turbulent zone.

1. Apparatus for mixing of a chemical medium in gaseous or liquid statewith a pulp suspension, comprising a housing having a wall that definesa mixing chamber, a first feeder for feeding the pulp suspension to themixing chamber, a rotor shaft, that extends in the mixing chamber, adrive device for rotation of the rotor shaft, a rotor body, that isconnected to the rotor shaft and arranged to supply kinetic energy tothe pulp suspension, during rotation of the rotor shaft by the rotationof the drive device, such that turbulence is produced in a turbulentflow zone in the mixing chamber, a second feeder for feeding of thechemical medium to the mixing chamber, an outlet for discharging themixture of chemical medium and pulp suspension from the mixing chamber,and a flow-restraining disk with one or more flow passages arranged inthe outlet from the mixing chamber to temporarily increase the flowvelocity of the pulp suspension when the pulp suspension passes theflow-restraining disk, the second feeder comprising at least onestationary feeding pipe that extends from the wall of the housing intothe mixing chamber, including an outlet for the chemical medium in or inclose vicinity to said turbulent flow zone, and the rotor bodycomprising a number of rotor pins which extend from the rotor shaft onthe upstream side of the flow-restraining disk.
 2. Apparatus accordingto claim 1, wherein the feeding pipe extends substantially radially tothe rotor shaft in the mixing chamber.
 3. Apparatus according to claim1, wherein the feeding pipe extends substantially parallel to the rotorshaft in the mixing chamber.
 4. Apparatus according to claim 3, whereinthe rotor shaft extends through the feeding pipe, whereby an annularoutlet for the chemical medium is defined by the rotor shaft and thefeeding pipe.
 5. Apparatus according to claim 4, wherein the feedingpipe extends coaxially or eccentrically to the rotor shaft. 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. Apparatus according to claim1, wherein the second feeder comprises a number of stationary feedingpipes.
 10. Apparatus according to claim 9, wherein the feeding pipesextend substantially radially to the rotor shaft.
 11. Apparatusaccording to claim 9, wherein the feeding pipes substantially parallelto the rotor shaft.
 12. Apparatus according to claim 10 or 11, whereinthe outlets of the feeding pipes are situated symmetrically orasymmetrically around the rotor shaft.
 13. (canceled)
 14. (canceled) 15.(canceled)
 16. Apparatus according to claim 12, wherein the outlets ofeach of the feeding pipes are of a non-rotational symmetrical design andat least one of the outlets is provided with an orientation of rotation(V1) in relation to the center of the rotor shaft that differs from thecorresponding orientations of rotation (V2) of the other outlets. 17.(canceled)
 18. (canceled)
 19. Apparatus according to claim 1, whereineach rotor pin is curved forward from the rotor shaft or backwardrelatively to the rotational direction of the rotor body.
 20. Apparatusaccording to claim 1 or 19, wherein each rotor pin has a width (b), asseen in the rotational direction of the rotor body, that increases alongat least a part of the rotor body in a direction against the rotorshaft.
 21. (canceled)
 22. (canceled)
 23. (canceled)
 24. Apparatusaccording to claim 1 or 9, wherein the rotor shaft is provided with anaxially flow generating element.
 25. Apparatus according to claim 24,wherein the axial flow-generating element comprises a number of blades,which are obliquely attached relative to the rotor shaft.
 26. Apparatusaccording to claim 24, wherein the axial flow-generating elementcomprises a screw thread or a band thread, which extends along the rotorshaft.
 27. (canceled)
 28. (canceled)
 29. (canceled)
 30. Apparatusaccording to claim 1, wherein each flow passage extends obliquely fromthe up-stream side of the disk against the center shaft of the disk. 31.(canceled)
 32. (canceled)
 33. Apparatus according to claim 1 or 30,wherein the disk is circular or coaxial to the rotor shaft (8, 104, 204,300, 406, 502).
 34. Apparatus according to claim 1 or 30, wherein thedisk is stationary arranged in the housing.
 35. Apparatus according toclaim 34, wherein the disk comprises a number of concentric rings whichare coaxial with the rotor shaft and at least one radial bar thatfixates the rings relative to each other and that are attached in thewall of the housing, whereby the flow passages are defined by the ringsand the bar.
 36. Apparatus according to claim 1 or 9, wherein the diskis integrated with the rotor shaft.
 37. Apparatus according to claim 36,wherein the rotor body comprises a number of pins, that extends from therotor shaft, whereby the disk is fixed to the pins on the down-streamside of the rotor body.
 38. Apparatus according to claim 37, wherein therotor body comprises an additional number of pins, that extend from therotor shaft on the down-stream side of the disk, whereby the disk isalso fixed to said additional pins (202, 408, 506, 506′).
 39. Apparatusaccording to claim 37, wherein the disk comprises a number of concentricrings which are coaxial with the rotor shaft, and the rotor pins fixatethe rings in relation to each other, whereby flow passages are definedby the pins and the rings.
 40. Apparatus according to claim 36, whereinspacer elements are arranged between the disk and the rotor pins.